Let's See if You Have Geometry Reasoning

Geometry Level 1

If PQRS is a rectangle and if 'A' and' B' represent the shaded areas (in the diagram above), which of the following statements is true?

A < B A = B A > B

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8 solutions

Mark Mottian
Jul 28, 2015

Let [ABC] denote the area of ABC

The diagonal PR divides the entire rectangle in half: [PSR] = [PQR]

So, [PEI] + [ESHI] + [IHR] = [PFI] + [FQGI] + [GIR]

The diagonal also divides two smaller shaded regions in half: [PEI] = [PFI] And [GIR] = [IHR]

It follows that [ESHI] = [FQGI] Or [A] = [B]

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Great problem. Loved it :)

Calvin Lin Staff - 5 years, 10 months ago

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Hey Calvin ! how are you ? I see you're master in Mathematics how you became good in Maths . give me some tips , I follow your answer always

Hadia Qadir - 5 years, 10 months ago

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Keep on practicing and improving regularly. Work on the "Problems of the day", which will help you get better over time. Read up on the wikis to learn about these techniques that interest you.

Calvin Lin Staff - 5 years, 10 months ago

Your method is much better than mine! :D

Kenny Lau - 5 years, 10 months ago

great solution

Rajan Thakur - 5 years, 10 months ago

but if PS=5 ,SR=10,SH=7 then IG becomes 3 if IH=2,then IF =3 which is not satisfying the condition

Saikiran Gunda - 5 years, 10 months ago
Kenny Lau
Aug 1, 2015

See Mark's image for the notation to use.

  • Note that PE = IF \mbox{PE}=\mbox{IF} and GI = HR \mbox{GI}=\mbox{HR} .
  • Note that the triangles PEI \mbox{PEI} and IHR \mbox{IHR} are similar.
  • Therefore, PE EI = IH HR \dfrac{\mbox{PE}}{\mbox{EI}}=\dfrac{\mbox{IH}}{\mbox{HR}}
  • By above, IF EI = IH GI \dfrac{\mbox{IF}}{\mbox{EI}}=\dfrac{\mbox{IH}}{\mbox{GI}}
  • By cross multiplication , IF × GI = IH × EI \mbox{IF}\times \mbox{GI}=\mbox{IH}\times \mbox{EI} , which is the result wanted,
  • since the area of A \mbox A is IH × EI \mbox{IH}\times \mbox{EI} ,
  • and the area of B \mbox B is IF × GI \mbox{IF}\times \mbox{GI} .
Jody Huneycutt
Aug 9, 2015

Any diagonal of a rectangle divides it in half. Therefore, the area of PRS equals the area of PRQ; and the area of PIE equals the area of PIF and the area of IGR equals the area of IHR. Since PQR is equal to PRS and if you remove the above noted equal areas from each, then the two areas left, A and B, must be equal.

Please refer to the figure shown by Mark Mottian: PEI+A+RHI = PFI+B+RGI Equation (1) Since: PEI = PFI Equation (2) RHI = RGI Equation (3) Substitute Equation (2) & (3) in Equation (1`) PEI + A + RHI = PEI + B + RHI Cancel: PEI, RHI Therefore: A = B

Shubham Jain
Aug 9, 2015

If we try to visualise triangle psr and pqr can be proved congurent by SAS and the triangles forming within these triangle (unshaded area )Are congurent now if equal are if taken off from congurent triangle the left area if also equal . We can prove the congruence easily and it is visible very much i hope i dont need to explain that

Wolfred Moonlake
Aug 5, 2015

In a short, rough, unofficial, initial analysis, I have concluded that: EI > FI > IG > IH (use sir Mark Mottian's image of solution as reference since I have only judged it mentally, so, there is no drawing / image to upload.) Then, the two rectangles are being separated by a diagonal inside a rectangle. Area of Rectangle EISH = (EI)(IH) and Area of Rectangle FQIG = (FI)(IG). Rectangle EISH uses the longest and the shortest division of the proportion (Extremes), and Rectangle FQIG uses the 2nd and 3rd longest division (Means), so I have concluded that they must be equal. (Though I still tried to properly solve it using ratio and proportion like what sir Mark did to confirm if I am indeed correct, and, I am.) This is only possible because the two rectangles were separated by the diagonal inside of the biggest rectangle. I apologize for my bad and confusing grammar, though.

Hadia Qadir
Aug 5, 2015

No trig PSR and trig POR will be equal. the left over traingles wil be same area , hence A =B

Calvin Lin Staff
Jul 31, 2015

See Mark's image for the notation to use. Consider rectangle IGRH, and let that have area C.

By similar triangles, I H P S = H R S R \frac{IH}{PS} = \frac{ HR}{SR} .

Hence, C A = H R S R = I H F H = C B \frac{C}{A} = \frac{ HR}{SR} = \frac{ IH}{FH} = \frac{C}{B} .

Thus, A = B A = B .

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